The present invention relates to electronic pointing devices and writing implements, and more particularly to styli for use with graphic tablets such as touchpads.
In the art of touchpads, it is conventional to provide a thin, flexible membrane as an outer member to be contacted by a stylus that is held by a user of the touchpad. A particularly vexing problem with this arrangement is that the flexible membrane, in order to permit high-resolution pointing and/or writing, is typically very thin and delicate, being particularly subject to damage in the event that the user subjects the touchpad to significant impacting contact by the stylus, which necessarily also has a fine point for operating the touchpad at high resolution.
It is known to use a conventional ball point pen cartridge as a stylus point, when it is desired to produce an inked record (such as on a paper strip temporarily covering the touchpad). When the cartridge is in good condition the rolling action of the ball avoids sliding contact wear of the membrane and/or the cartridge. However, when ink is not desired, an empty cartridge generally does not provide this advantage because the ball normally fails to roll. More importantly, the touchpads in use are still subject to excessive damage even when the stylus incorporates a ball pen cartridge.
In my previously-filed patent application (U.S. patent application Ser. No. 10/186,323, now U.S. Pat. No. 6,972,754), I disclosed a touchpad stylus which provides smoothly increasing axial displacement of the stylus member of up to approximately 0.05 inches in response to axial loads ranging from approximately 0 to up to approximately 200 grams. This touchpad stylus was based on the general belief that the “normal” pressure applied by a signator is typically less than about 200 grams. Recent test work, however, has revealed that a number of individuals occasionally press down against a touchpad with increased force, such as between 200 grams and 500 grams and occasionally between 500 grams and about 1000 grams.
Accordingly, there is a need for a touchpad stylus that does not suggest outer membranes of touchpads to excessive damage even when forces of between about 200 grams and about 1000 grams are applied.